Dec 152017
 

The difficulty in writing a 2017 final blog is to avoid reviewing the year as that will occur with the Annual report. None the less I must cover some matters that have highlighted the year. The first is the great fishing year that we have had and are still having though the focus has moved from the river to the lake. The second is that Simon Stewart has completed his PhD thesis. 

Of immediate importance is the warning of the toxic algal bloom that has occurred in areas around the lake. TDC has put up signs at affected areas . The following notice was sent to me on 7th December by Rosanne Jollands, TDC counsellor.

Algal bloom key messages
Dense mats of potentially toxic algal species have been found at multiple sites around Lake Taupō.

It is a naturally occurring phenomenon in hot and sunny weather, as we have experienced over recent weeks, but they also depend on other factors such as the amount of available plant nutrients, phosphorus and nitrogen.
Overnight testing by NIWA has confirmed the presence of Phormidium algae at Five Mile Bay, Acacia Bay, the main lakefront in Taupo, Whakaipo Bay and Kinloch Beach. Due to weather conditions other areas may become affected and the public should be vigilant.

The Medical Officer of Health from Toi Te Ora Public Health has issued a health warning for the public to avoid paddling, wading, swimming or any recreational activity that may bring them into contact with the algae mats, which can accumulate on the shoreline. Pets and livestock should also be kept out of the water and off the shoreline.
Symptoms of contacting the mats can include skin rashes, stomach upsets, and respiratory issues; ingesting algal material can cause neurological symptoms such as numbness and weakness, visual symptoms and in severe cases affect the ability to breathe.
Taupō District Council has comprehensive monitoring in place to ensure the quality and safety of all drinking water at all times.

Just before posting this blog I am advised that the notifications of toxic algal bloom have been withdrawn.

Fishing

It has been a great year for anglers. Good sized, good conditioned fish and plenty of fish. I saw a few 5lb Rainbows and a couple of browns bigger than 7lb and I heard of even bigger fish. The action has moved from the river to the lake but there are still good fish in the river and anglers trying to catch them. I have had excellent lake fishing.

The Lake level remains high and it is important to know that the 200 meter mark is from the line between the poles currently out in the lake. The 200 meter  zone is for fly fishing only.

The road to the Blue Pool remains closed to anglers at this time.

PhD study

I had a pleasant chat with Simon Stewart this morning. Simon had at the end of November returned from a meeting of the Global Lake Ecological Observatory Network (gleon) held in New Paltz, New York state. His work is attracting attention amongst fresh water scientists. I asked Simon to be our guest speaker at or AGM probably in late April to which he has tentatively agreed. He is pleased to have completed his thesis and looks forward to enjoying a break with his family.

Lakes Waterways Action Group (LWAG)

The last LWAG meeting was held 18th November 2017 in Taupo. The information from the guest speaker, Dr Piet Verberg, Hamilton NIWA, gives a valuable insight into the mixing of Taupo water among other matters. I hope that you find the information valuable.

Jane Penton, LWAG secretary makes extensive notes. I have copied her notes here.

4. ‘Lake Taupo Research’
Piet introduced himself saying he had been at NIWA for 9 years. Previous to this he worked in East
Africa & North America. He expressed thanks to Tuwharetoa, the Lake Taupo Management Board &
WRC. Outlining his talk including; 1. Lake buoy, 2. Lake Taupo long term monitoring Project, 3. Nutrient
limitation experiments & 4. New research program on trace elements effects on algae – growth may
be limited.
1) Lake Buoy Technology: 2015 – automatic monitoring station installed so as to have a better
understanding of how Lake works, especially relationship between vertical mixing and food web,
including health of trout. Buoy anchored in same place 50 m down and has above and below surface
Lakes & Waterways Minutes – 16 November 2017
monitoring systems. Buoy has to withstand mechanical action of waves so has two heavy anchors and
two surface buys.
21 water temperature sensors operate at different depths. Also four oxygen sensors – keep track of
depletion of oxygen in bottom level. Chlorophyll a at surface (plus more near surface). Above surface
– weather station; wind speed/direction, relative humidity, air temperature, air pressure, rainfall,
incoming longwave radiation etc. Frequency: per minute.
Water temperature: (Slide showing whole year March 2015 – March 2016). Winter – temps at suri’ace
same as bottom as lake fully mixed – lasted about two months. Further slide showing week that lake
mixed. Mixing very important for replenishing oxygen in bottom level of lake, also for replenishing
nutrient layer. Summer; nutrients in bottom level build up as nutrients come down from top layer,
decomposing & mineralising. End of summer – higher in bottom. Then, mixed up to surface in winter
and used by algae to grow. Chlorophyll o means algae bio-mass – always higher in winter, by a factor
of 5 in Taupo. Better mixing and longer mixing period means a good year for trout. (Graphs shown)
Daily mean dissolved oxygen – after winter when lake stratified/warms & separates in layers – oxygen
in deep water decreases throughout summer. Also in surface – in equilibrium with oxygen in
atmosphere. Oxygen determined by temperature. Oligotrophic lakes show 100 meter depth – oxygen
is higher than at surface. ‘Othograde’ oxygen distribution-oxygen levels higher in bottom waters than
surface waters.
Oxygen variability over the day (Graph showing variations over a day) related to photosynthesis –
oxygen goes up & respiration – oxygen goes down. Difference between photosynthesis and respiration
can calculate productivity (algorithms used). Atmosphere – relationship considered due to data from
weather station on buoy.
Monthly means (graphs shown – one year period) Weather station c/f/ Taupo and Turangi weather
stations. Wind speed higher on lake. Also air temperatures higher on lake; on average – 2% higher
than Taupo airport.
Temperatures of air and water surface. Water temp on average 2% higher than air – warms air over
lake. Monitoring data of last 20 yrs; Taupo lake surface and air temps average 2% difference.
Importance re; energy flows. Wind speed and difference between temps air/water – c/f heat loss.
‘Global Heat Balance’ – in by solar radiation and lost by evaporation. Incoming radiation and
evaporation fluxes determined through data collected. Paper published recently on this-c/f Lakes all
over world. Data provided to harbourmaster; wind speed, air temp etc. This is renewed every hour
and Tuwharetoa get a similar display.
Lake Buoy Summary: High frequency, real time data from deepest monitoring buoy in NZ. Better
understanding of drivers of algal biomass. Also allows a good understanding of the duration and
intensity of the annual mixing period – more intense and longer. Increased winter mixing makes Lake
Taupo more productive.
2) Long Term Monitoring: ‘Effects of climate warming – what happened in Lake Taupo and why?’
Many lakes all over world have warmed in last couple of decades and at faster rate than air temp
Average – half a degree per decade. Locations shown (map) – only a few didn’t warm including Lake
Rotorua & Lake Taupo. (Piet provided data on Taupo for this study) Average summer temps didn’t
increase and winter temps decreased slightly. Not many lakes with good time series for temp. Rotoroa
(small lake in Hamilton) warmed .5% per decade – similar to other lakes globally.
Climate warming effects on lakes: Reduced mixing, lower nutrient supply, decrease in plankton near
surface. Less nutrients from deep water- more stratified.
Lakes & Waterways Minutes – 16 November 2017
Lake Taupo water temp (graphs). From global trends; expect winter mixing period to become shorter
but this hasn’t happened in Taupo. Negative trends in temperatures in upper 50 meter and positive
trends in depth below 50 meter. Lower depths increased. Temp difference has become smaller and as
a result lake can mix more. Less density in water – easier it mixes. Temp gradient decreased
significantly-difference between top and bottom. Number of days > 0.3 degrees increased (doubled).
Mixing period has doubled. Opposite effect to climate warming.
Causes? Either by cooling at surface or increased warming at bottom e.g. change in geothermal
sources, changes in weather patterns or wind speed, or changes in volume/temp of tributaries.
Looked at data from buoy – air temps haven’t changed. May have something to do with increased wind
speeds, however. Although in this area expected to decrease with climate change effects.
Increased geothermal heat flow? Highest heat flow site is a 4 square meter area – don’t know if there
has been any change. Looking at possible indications – uplift at Horomatangi reef happened mid 80’s
then relatively stable, then 90’s then 2008. Not much relationship with Lake evident. Earthquake data
since 1990 analysed – high activity in 90’s and 2008 but not much of a trend observed. Chemistry –
geothermal vents release heat and dissolved solids. Annual means of monthly data at Taupo gates.
Arsenic has increased sharply – but not a good indicator of geothermal releases. Relationship with
sediments complex. Solids and productivity increased. Only collected data at Taupo gates from 1994
-2014.
Effects of increased river temperatures? Temps in rivers have all increased. Average 11 – 12 % (not
very high) – most enter into deep water – could have warming effect on bottom waters. Effects?
Bottom water phos -150 m depth. (Graph 2004 – 2015). More Lake mixes, more of these nutrients
return to surface. Higher peak in algal biomass in winter and spring when lake mixed. This drives
consumers/fish populations.
Winter surface concentrations – enhanced nutrient in surface layer. Past20 yrs – chlorophyll
increased. Correlation between surface, bottom water- higher algal biomass.
Conclusions: Chlorophyll increased in winter& stratification decreased. Winter mixing period
increased. Causes: Increased wind speed? Increased geothermal heat flux? Warmer river water?
Effects: Increased return of dissolved nutrients to surface layer, increased algal biomass during winter,
Lake management implications – may want to take this into account for planning of Lake water quality
protection.
3) ‘Evidence of P Deficiency in a large N limited lake’: Grant received for NIWA study & for visiting
scientist from University of Minnesota Duluth, Large Lakes Observatory in 2015. Measurement of
samples taken from deep buoy site.
Lake Taupo facts: Altitude 357m, Lake Area – 612 km2, Catchment – 2849 km2. Water Renewal -11
years. Mean depth – 97m, Max depth – 165m, Mean Secchi – 16m. Lake Taupo is described as warm
monmictic, mixing completely July-August and Ultraoligotrophic. Stratified period – oxygen doesn’t
increase much. So good for trout due to being oligotrophic. NZ Lakes considered N limited – low in N
and low in ratio with Phos. More likely to be N limited C/F rest of world – NZ exceptional.
Prior studies to examine nutrient deficiency in Taupo: White and Payne 1975-76 looked at response
ofalgaeto N and phos at different times of year. Early 80’s – another study showed no response to N
and phos but used different measures. 1986 – a weak response to N and no response to phos evident.
Around 2000 nitrogen fixing cynobacteria were becoming more prominent in Lake Taupo leading to
concern about nutrient enrichment.
Lakes & Waterways Minutes 16 November 2017
Another study (Hall et al 2002), to determine limiting nutrient in Taupo found that; N stimulated
chlorophyll while P did not, N & P together gave a stronger response and concluded N was limiting in
Lake Taupo. Study made over whole year.
2015 NIWA study ‘Is Lake Taupo still N deficient?’ – Used different methods – 7 indicators including;
QChl-general (carbon to chlorophyll in algal cells), C:P, N:P, APA, P debt- P deficiency & C:N, N debt
– N deficiency. Enrichment bioassays studied.
Nutrient status indicators tested in lakes with different N:P ratios; 28 lakes f varying nutrient loadings.
Indicators were consistent with whole lake responses to N and P loading.
Great Lakes Experimental Lake Area (ELA) in Ontario; Lake 227 – nutrients added e.g. barrel of
phosphate in 2011. (Pic shown). Experiment running since late 60’s i.e. for more than 40 yrs.
Interesting results observed.
Lake Taupo – 14th Jan, 20th Jan, 02 Feb 2016 – indicators of nutrients analysed: Temp, Fluorescence,
Euphotic zone. 10m, 30m and 50 m depth – scope. (Graphs shown) Nutrient levels low at that time of
year. N always below detection limit. Chlorophyll increased during sampling – deficiency of nutrient
in Lake. Phos deficiency – especially in surface layer. Also some N deficiency, sometimes strong in deep
water.
Lake Taupo Bioassay-growth experiment showed very little response to adding N but strong response
to phos. Different to 2001 study. Comparison of 2015 study with previous studies; samples taken at
same time. Changes evident – best explained by monitoring data from 1994 taken every 3 weeks. N
has increased. However N became less limiting 2001 – 2015. Lake Taupo now phos limited. Lake Taupo
annual means: Ratio PC:PN. (Proportion of nutrients – N and phos in algal cells). Since 1999 data
showed that Phos more limiting and N less limiting.
P deficiency was demonstrated in Lake Taupo in 2015. This is consistent with long term monitoring
record of N:P. Legacy of increase of N as expected has unbalanced the nutrient regime of Lake Taupo.
Comes in through groundwater – long resident time and is the result of activities in catchment several
decades ago. Imbalance of nutrient regime in lake.
Acknowledgements for study listed including: Tuwharetoa Maori Trust Board, Taupo Harbourmaster
for enabling the 3 weekly sampling and installation of buoy, WRC for contracting NIWA’s monitoring,
and team of technicians including Max Gibbs – who ran programme for 19 yrs. (Piet took over two
years ago.) Piet said Max made sure Taupo had the best monitoring programme in country. Methods
have been kept consistent over 23 yrs- allowing comparison over decades.
4) New Project: Trace Metal Limitation of Phytoplankton Growth in NZ Lakes’: All algae need trace
metals (TM’s), especially cyanobacteria. (Diagram showing interactions between phytoplankton and
nutrients and the effect of nitrogen load reduction in lakes).\f there are not enough TM’s for the
cyanobacteria, then N load reduction would not result in more cyanobacteria. Issue around Lake
Taupo – cobalt-deficient soils; ‘bush sickness’ – 1930’s found deficiency of cobalt in Taupo volcanic
zone. Now can farm due to added to fertiliser. Affects large area – volcanic soils including Taupo and
BOP. Lakes low in trace metals as well which may affect algal growth – extra tool to manage algal
growth in lakes. Not understood by Lake managers; WRC – report stated that this has not been
measured in Taupo. Iron & manganese measured by Eddy White – low concentrations. Waikato River
water quality monitoring programme includes trace metals.
Sample technique specifically needed – began last year and found level in even lower concentrations
– typically below detection levels. Funding $1M for 3 year project from MBIE’s Endeavour Fund. Also
BOP & Te Arawa Lakes Trust. Trace Metal Limitation of Phytoplankton Growth in NZ Lakes’ study has
other collaborators including international institutions e.g. University of Geneva, International Atomic
Lakes & Waterways Minutes – 16 November 2017
Energy Agency, Monaco and the University of Minnesota. Dr lan Kusabs working with stakeholders
and responsible for dissemination of research.
Trace metal CTD Rosette system for sampling of full depth profiles on the larger lakes. (Pic shown)
Specialised laboratory; trace metal clean (shipping) container (pic) at NIWA in Hamilton. Instruments
at University of Otago for analysis of low trace metal concentrations, (pic) Algae and trace metals
added in small concentrations – see how they grow. TM incubations and a response graph showing
maximum quantum yield- values of phytoplankton cells after 18 h exposure in response to
combinations (pics & sample graph}.
Questions:
Eddy White’s daughter introduced by Paul – Kathy White Q-re; science findings implications for LTPP
Joint Committee? Piet-a little worried about phos – enhanced mixing. More attention to phos needed
– keep an eye on how this changes and effect on algal biomass. Hopefully N goes down when peak of
N reaches Lake – will go down as predicted by Bill Vant. Kathy Q – timeframe? Piet -decades. Nick Q
– with cobalt added to fertiliser – has this affected algal growth – e.g. bloom in 2000? Piet –
cynobacteria in Lake N limited.
Since then cynobacteria has declined now that Lake is not N limited. Cobalt in fert – yes may limit
growth of algae – need to be more careful. Can this be managed more carefully? Still needed against
effects of ‘bush sickness’. Nick Q- if Lake more phos limited than N – effects of waters from northern
area mean an N increase. Regarding increasing biomass if Phos limited – adding N won’t make more
difference. Piet – agrees. If phos doesn’t increase, then less worry about N increase. Urlwyn – with
more phos coming up, are we likely to see differences re N limited/phos limited over time? Piet –
mixing brings more phos. Nutrients have different pathways – more N from groundwater. Q – Long
term? Piet-will plateau, then go down. Timescales more to do with catchment hydrology. On average
– 2 decades. Paul – maybe a little more. Piet – related to this; When was land used at most intense?’
Q-Trace metals analysis-fluxes from tributaries receiving fert? Piet- measuring trace metals in Lake.
3 parts – in middle of lake. Project doesn’t have scope for incoming waters. Preliminary project – if
significant. Managers will look at his more closely. Concentrations in lake; will decide whether this is
low enough to limit growth. If growth enhanced by adding more minerals = limited. Many different
trace metals plus phos and N. Composition of nutrients/minerals dictates species of algae.
Q – Enhanced N levels – shallow areas more weed likely? Piet – seems possible if N limited. Not sure
if these are N limited or not.
Nick -1934 Dr Armstrong recorded visibility to 220 feet (70meters). Current – 65-70 (18-20 meters).
If secchi depth 220 feet – clearest recorded visibility in world? Piet – it is possible -wishes there were
more measurements between then and 70’s when DSIR started measuring. Pure water-theoretical
80 meter max – if true close to maximum. Don’t’ know of any deep lake with this level of visibility.
South Island’s Blue Lake only 3 meter deep – one of clearest in world. Crater Lake in Oregon – 60 m so
theoretically possible.
Q – Phos; how much in sediments? Risk if period of mixing increased? Piet – lots of phos in sediment
so yes a risk. Sediment cores – need to work with data. Measured phos – dangerous; what allows it to
be released? However, low oxygen situation is not likely to happen in Taupo. In sediment in lake, phos
comes in at different times. Phos bound by calcium and hard to release (80 % in Nth American lakes)
but in Taupo – easily releasable. Q – Increased mixing will decrease risk? Piet – yes.
Q- Interested that no monitoring ofgeothermal influence. Buoy location? Piet- regular monitoring
has been done at same site since 70’s. Fairly central and accessible. Would love to have more buoys
Very expensive including maintenance (NIWA). Can see exchange of water from one end to other.
Lakes typically seiche so would be good to measure effects of this.
Lakes & Waterways Minutes – 16 November 2017
Giff Q – re; calcium locking phos – how does this compare with alum? Piet – yes similar process.
Giff Q- cleaned Lake Rotorua in 3 yrs but Iwi stopped it. Piet – if bound to calcium, can release when
anoxic although not all, or that quickly. No release with alum.
Paul Observation – LWAG helped to sponsor Waikato Universit/s Bio fish study with Mercury & TDC
& private donors. Analysis of temp measurements – shallow waters in bays warmer than deep lake.
Could be relationship with temp and algae – concern of locals. Q re; Deep chlorophyll maximum (DCM)
– how is this behaving regarding increase N and mixing over time? Piet – less nutrient limited than
surface layer. Higher biomass in DCM- not much light but more nutrients from deep water. Increase
of N – less effect on DCM than elsewhere. Paul – David Hamilton and other scientists believe DCM one
key indicators of Lake health – do you agree? Piet – yes, only get this in clear lakes. Typically DCM
occurs around or below bottom of mixed layer. If Lake is not clear-euphotic zone shallower. Deeper
euphotic zone the more oligotrophic the Lake is. So yes could be indicator.
Thanks to Piet.

 

Thank you to our members.

Wishing you a Merry Christmas and all the best for 2018.

Eric Wilson

Secretary

 

 

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